The following relates to the industrial processing arts, industrial safety arts, controlled atmosphere processing arts, and related arts.
Certain types of industrial processes generate pyrophoric particles. For example, in the nuclear power industry, some components are selected to be constructed of zirconium alloy material due in part to low neutron absorption characteristics of these alloys. However, high temperature processes such as welding, cutting, and so forth applied to zirconium alloy material can not only be corrosive to material performance if done in an oxygen environment but further tend to generate zirconium alloy particulates regardless of fabrication environment. In an oxygen environment the higher surface area-to-volume ratio of these particulates compared with the bulk material enhances their oxidation characteristics to a point where these particulates become flammable and can spontaneously combust in air or in response to a spark or other ignition source. Accordingly, for these and other reasons such processing is typically performed in an inert atmosphere such as an argon atmosphere. However, the generated pyrophoric particulates must still be dealt with.
Historically, the process exhaust was vented to atmosphere. An ignition source might be included in the chimney or vent to encourage burning of any pyrophoric particles. However, airborne metallic particulates can cause respiratory problems and raise other environmental concerns. Accordingly, modern processing methodologies filter out the metallic particulates, including pyrophoric particulates, from the exhaust stream prior to exhausting to atmosphere.
The filtering of metallic particulates is performed using wet scrubbers and/or dry filters. In the case of zirconium alloy processing a conventional approach is to employ a wet scrubber to capture most pyrophoric particles, followed by a dry filter for final cleanup prior to exhausting to atmosphere. However, in processes that generate high concentrations of very small pyrophoric particulates, the wet scrubbers are not highly effective. For example, in some zirconium alloy processes greater than 50% of the pyrophoric particulates are smaller than 1 micron in diameter, and these small particulates are not effectively removed by the wet scrubber. In such cases, the dry filter accumulates pyrophoric particulates rapidly, and must be replaced on a frequent basis—failure to do so can result in spontaneous combustion of pyrophoric particulates in the dry filter and possible fire and/or explosion.